one 256 vs two 128 SDRAM DIMMs

Hi Gang!

Please allow me to risk initiating a great theoretical debate ala 'Internal vs. External Modem' or 'System Off vs. Always On'. Here goes ...

What are the advantages and disadvantages to using 'one 256 MB DIMM' vs. 'two 128 MB DIMMs'?

Assumption: SDRAM Manufacturer, Price, Quality, and Speed are Equal.
Assumption: Motherboard CAS-2, Bus ratio, 4-way Interleaving are constant for both scenarios

1) Is there any performance issue with SCENARIO-2 that relates to the fact that the motherboard needs to address two physical DIMM slots instead of one?

2) Likewise, does the single 256 MB module itself contain some optimized design for accessing its larger chips that in effect trumps the architecture of the motherboard implementation of multiple DIMM slots? (Perhaps this explains the counterintuitive slightly higher price for SCENARIO-1?).

3) Gut instinct tells me that there are obvious disadvantages to SCENARIO-2: such as power consumption and heat generation. Is this penalty substantial enough to effectively make SCENARIO-2 less desireable?

4) Gut instinct also tells me that since no two parts are EXACTLY identical (the two 128 modules), there may be some slight electrical variation between the two 'identical' 128 MB DIMMs that might somehow affect performance in SCENARIO-2. Or, am I all wet on this one?

5) Does 'interleaving' (which I don't fully understand) factor into the 'one DIMM' vs 'two DIMMs' scenario?

I just wonder if anyone has performed any carefully controlled experiments with some precision benchmark that would shed light on this.

Sarah McIntyre
7 answers Last reply
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  1. The only difference between 2x 128MB or 1x 256MB is you have one less DIMM slot left with getting 2x 128MB. If there is any difference it would be so slight you wouldn't notice it. CAS2 from what I have read is 5-10% faster than CAS3.
  2. Well if you are using one stick, thats one less component on the MOBO, dunno how much power is consumed, maybe less stress on the power supply in the long run. I dunno just an assumption.
  3. If you're a girl, you're the coolest girl on this forum! :)

    Power consumption should never be considered an issue, heat dissipation should also never be considered an issue. Unless you take the RDram example, or your talking about notebooks.

    If you want to talk about electrical difference between the 2 DIMMs then you should also talk about the difference between each chip on the single 256MB DIMM.

    This should never be considered an issue because all power supply at those stages are paralleled, from the DIMM slots to the every single chip.

    The only consideration I have is that since 2 DIMMS uses more pins therefore the communications should be faster. But in reality that is now the case. Electronics doesn't work like this.

    Best regards
  4. Well Gal I would have to say that 2 sticks are better than one! really only because when I was looking for mem @ Mushkin they didn't regard to 256 stick to be up to spec. Not sure if still the case but it was right on there site. I was looking for the least trouble with the finiky AMD cpu.
  5. If you only have two memory slots and you think you'll upgrade beyond 256mb anytime soon, get the 1 256mb stick. Otherwise 2 x 128mb is adequate.
  6. Are there any new opinions on this issue? I dropped my old Soyo SS7 computer down to 256 MB of system ran in order to get my ram back in its cacheable range. I have an extra 128 that I am going to add to my mother's computer. She has an identical 128 stick. Should I keep my 256 stick or give it to her and add the two 128s to my computer. I do a lot of 3D gaming and push my K6-2+ 550 (overclocked to 600 MHz) to its limits... I have read that 2 sticks are better than one...

    <font color=red><b>To reign is worth ambition though in Hell:
    Better to reign in Hell, than serve in Heav'n.</b></font color=red>
    John Milton, <i>Paradise Lost</i>, II 262-263
  7. Some boards will overheat some modules when the most agressive timings are choosen, due to heat buildup between the modules. Also, if your memory is near the edge at the fastest settings, using two module could cause a problem due to increased latency involved when using multiple pathways. Both problems only occur when the memory is right near the edge of stability anyway, but I like to run everything at it's quickest settings. In fact, I had to space my modules apart in order to prevent heat buildup, and I have top quality memory.

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